Air-circulation apparatus for self-cleaning oven and the like

ABSTRACT

An electric motor mounted in a compartment adjacent an oven or other food-treatment chamber carries a pair of centrifugal fans, one in the chamber and one in the compartment. Each fan has on each axial face an array of radially extending vanes or blades. The two central arrays of vanes confronting each other flank the outlet of a conduit open at its inlet to the ambient atmosphere so that air is drawn in through the conduit, then drawn axially in both directions, into the chamber and into the compartment, and then expelled radially to form a gas barrier at this opening. The vanes turned toward the motor draw cooling air in over this motor and the vanes directed into the chamber circulate the gases therein. The fans are rotationally coupled together only by a few angularly spaced bolts, in the cooling-air stream, surrounded by sleeve-like insulating spacers, to prevent heat conduction back to the motor.

United States Patent Jung et al.

[151 3,656,469 [451 Apr. 18, 1972 [54] AIR-CIRCULATION APPARATUS FORSELF-CLEANING OVEN AND THE LIKE [72] Inventors: Anton Ladislaus Jung,Herborn; Erhard Ledwon, Guntersdorf, both of Germany 3,529,582 9/1970Hurkoetal ..l26/21A 3,530,278 9/1970 Tilus ..l26/21RX PrimaryExaminer-Charles J. Myhre Attorney-Karl F. Ross [57] ABSTRACT Anelectric motor mounted in a compartment adjacent an oven or otherfood-treatment chamber carries a pair of centrifugal fans, one in thechamber and one in the compartment. Each fan has on each axial face anarray of radially extending vanes or blades. The two central arrays ofvanes confronting each other flank the outlet of a conduit open at itsinlet to the ambient atmosphere so that air is drawn in through theconduit, then drawn axially in both directions, into the chamber andinto the compartment, and then expelled radially to form a gas barrierat this opening. The vanes turned toward the motor draw cooling air inover this motor and the vanes directed into the chamber circulate thegases therein. The fans are rotationally coupled together only by a fewangularly spaced bolts, in the cooling-air stream, surrounded bysleevelike insulating spacers, to prevent heat conduction back to themotor.

12 Claims, 4 Drawing Figures PATENTEDAPR 18 m2 3, 658,469 sum 2 [IF 2 INVENT CR5 '3 n fan L, Mum E rhea/(I Ledwon BY (R 58 AttorneyAIR-CIRCULATION APPARATUS FOR SELF-CLEANING OVEN AND THE LIKE FIELD OFTHE INVENTION The present invention relates to an oven. Moreparticularly, this invention concerns a self-cleaning oven having aninternal blower for circulating air and distributing heat duringcleaning or cooking.

Such an apparatus is described in our commonly assigned patentapplication Ser. No. 40,128 filed May 25, 1970 and entitledSELF-CLEANING OVEN WITH INTERNAL AIR CIRCULATION.

BACKGROUND OF THE INVENTION The blower in a self-cleaning oven effectsan equal distribution of the heat in the oven during baking or roastingfor more regular cooking and during self-cleaning for pyrolyticdecomposition and/or oxidation of food residue even in so-called dead"corners of the oven.

A persistent problem with conventional ovens of this type is the thermalprotection of the blower motor. During self-cleaning, when temperaturesin the neighborhood of 400-500 C are common, this protection is of greatimportance since such heat can easily destroy most motors. In order toovercome this difficulty the motor can be mounted outside thefood-treatment chamber with its drive shaft passing through the ovenwall, the fan being mounted on the end of the drive shaft. Such asolution creates a further problem: the prevention of gas leaks aroundthe shaft. The gases developed during a selfcleaning operation areodorous and dangerous and cannot be allowed to return to the kitchen. Inaddition heat is conducted back along the motor shaft to the motorarmature, often damaging it.

OBJECTS OF THE INVENTION It is, therefore, an object of the presentinvention to provide an improved apparatus for thermally treatingcomestibles, particularly in an oven of the self-cleaning type.

Another object is to provide such an apparatus which overcomes theabove-mentioned disadvantages.

SUMMARY OF THE INVENTION These objects are obtained, in accordance withfeatures of the present invention, by an apparatus having afood-treatment chamber in which a food-treatment temperature can beestablished, and blower means having a drive motor carrying a rotorincluding centrifugal-fan means arranged to circulate the gases in theoven, to draw gases into the chamber, and to draw a stream of coolingair over the blower drive, i.e. an electric motor.

According to a further feature of the present invention a compartment isprovided adjacent the food-treatment chamber, and a pair of fans isprovided, one in the chamber and one in the compartment. Each fan iseffectively formed as a pair of back-to-back centrifugal fans so thatthere are altogether four different arrays of vanes, two directedaxially in toward each other, and two end ones directed axiallyoutwardly.

In accordance with another feature of this invention the end array ofradially extending vanes directed toward the motor serves to draw acurrent of cooling air into the compartment, over the motor. The otherend set of radially extending vanes directed into the chamber circulatesthe hot oven-cleaning or food-treatment gases in this chamber. The twocentral, confronting sets of vanes flank a dividing wall between thechamber and the compartment, an opening being improved in this wallwhich permits the two fans to be connected together and forms an annulargap around the connection. A conduit is provided having one end open tothe ambient air and the other end open in the compartment between theone fan and the wall, just adjacent the annular gap. In this manner thetwo central fans draw the air axially in both directions and expel itoutwardly. These two sets of vanes have relative gas-displacingcapacities which create a pressure differential across the opening inthe wall to draw the air mainly into the oven muffle, with only a minorportion being drawn out into the cooling compartment. In this manner agas barrier or gas lock is formed at the opening in the wall to preventthe noxious oven gases from escaping. A catalytic afterbumer, accordingto another invention feature, is provided to process the oven gasesduring self-cleaning and cooking.

According to yet another feature of the oven, the fans are not simplyfixed on a common motor shaft, but are rotationally coupled togetheronly by several connector bolts which are radially spaced from therotation axis and angularly spaced from each other. Insulating spacersleeves are provided to hold the separate fan elements apart, andthereby to prevent direct heat conduction. These bolts are providedbetween the two fan elements constituting the fan in the compartment sothat the motor is coupled as indirectly as possible to the fan elementsor sections in the oven muffle itself. Moreover, the bolts lie in thepath of the cooling air.

The present invention is applicable as well for any air circulatingsystem in which hot air or even a cold-preserving or freezing gasstream, e.g. volatilized from liquid nitrogen, is to be brought intocontact with goods in a chamber. Thus the invention, in its most generalsense, comprises a treatment chamber in a wall of which is mounted thefan arrangement of the instant invention. The fan arrangement comprisesa first axial-intake radial-outflow blower disposed within the chamberand drawing the circulating treating gas axially inwardly andcirculating it radially outwardly within the chamber. A secondaxial-intake, radial-outflow fan within the chamber, advantageouslyprovided on the opposite surface of the first fan, draws thetreating-gas stream into the chamber and advantageously has a capacitysubstantially less than the volume rate of flow of the circulating fanso that only a minor proportion of fresh treating gas is induced to flowinto the chamber by this second fan in comparison with the quantity oftreating gas continuously recirculated within the chamber per unit time.The fresh treating gas may be air or a preserving or deep-freezingfluid, such as liquid nitrogen, which is drawn into the chamber througha duct system independent of the cooling arrangement to be describedhereinafter. This duct system communicates with the chamber immediatelyadjacent the second or intake fan described above.

The fan arrangement, in which all of the blower devices or impellers aredriven from a single source and are rotatable about a common axis, alsoincludes a third axial-intake, radialoutflow fan positioned close to thegas intake fan and the duct arrangement mentioned above to divert partonly of the fresh gas from the inlet stream away from the chamber andinto the motor compartment to form thereby a gas lock as mentionedearlier. This fan creates a cooling stream which flows around the fewbolts securing the fans in the chamber to the fans in the coolingcompartment. The fourth fan, which may have a volumetric capacitysubstantially greater than the second and third fans, but generally lessthan that of the first-mentioned, is

' also of the aixal-intake radial-outflow type and cooperates with acooling conduit which opens into the cooling compartment generallyaxially and surrounds the drive motor of the system to created an influxor primary cooling stream which cools the motor. The radial outflow fromthis fourth fan can be diverted into the atmosphere without danger andadvantageously is combined with the minor cooling stream from the thirdfan mentioned earlier.

DESCRIPTION OF THE DRAWING The above and other objects, features, andadvantages will become apparent from the following description,reference being made to the accompanying drawing, in which:

FIG. 1 is a longitudinal vertical section through an oven according tothe present invention;

FIG. 2 is a longitudinal horizontal section of the oven of FIG. 1;

FIG. 3 shows in enlarged scale a detail of FIG. 2; and FIG. 4 shown inenlarged scale the detail indicated by arrow and circle IV of FIG. 3.

SPECIFIC DESCRIPTION The oven shown in FIGS. 1 and 2 basically consistsof a body 52 of insulating material defining an elongated chamber ormuffle 54. A metal shell 53 fits over the closed end of this body 52 anddefines air passages as will be described below. Received in the chamber54 is a rack 26 which is fitted at its vertical sides with food-trayslides 28 and has end walls 27 which are tapered as a hood and form aport 55.

A motor 2 is mounted in the compartment 5, this motor rotationallydrives the blower rotor 1 constituted by a cooling fan 7 in thecompartment 4 and a circulating fan 6 in the chamber 54. A hole 51 isformed in a rear wall 37 of the oven compartment, with the fansconnected together through this hole. An electric-heating element 41 isprovided for heating the chamber 54, although a burner can be used forthis purpose.

The oven has a door 17 at its end turned away from the compartment 4.This door is carried on a vertical hinge 24 and comprises three parallelplates 56, 21 and 22 of insulating material, the plates 21 and 22 beingcemented flatly together and the plates 56 and 21 being separated byshort legs 20 to form a vertically open space 18. The plate 56 has aperipheral heat-resistant seal 19 which fits against an internal rim 25of the oven opening 23 in a closed position of the door 17 to tightlyclose the chamber 54. Air blowing across the top of the upwardly openspace 18 draws air by the venturi effect through the door to cool it. Inthe absence of air blown over the top of the door, convection currentsof air in the space 18 provide the requisite door cooling.

At the closed end of the oven is a compartment 4 formed by the wall 53and perforated at 43 in its back wall 3 adjacent a stepped cylindricalsleeve 40 housing the drive motor 2 for the rotor 1.

As best shown in FIGS. 3 and 4, this motor 2 has a shaft 57 passingthrough a bearing 50 held by a spider (not shown) to the motor housing40. The shaft 57 carries a hub 58 having a face or side formed with aplurality of angularly spaced and radially extending vanes 11 whoseouter edges are all joined by an annular flange element 38 of curvedcross section. These vanes l 1 serve to draw air in through theperforations as shown by the arrows 47, and expel it outwardly as shownby the arrows 46.

Three angularly spaced bolts 13 (see FIG. 4) pass through the connectingelement constituted by the flange 38 and are screwed into bores inanother element formed by a flange 39 which is integral with vanes 12.Insulating spacers 61 formed with heat-radiating vanes 14 are providedon the bolts 13 to prevent heat conduction between the flanges 38 and39. A gap 62, traversed by cooling air which flows over the bolts andtheir sleeves, is thus formed between the two sections of the fan 7.

The flange 39 is part of a metallic generally cup-shaped body 36press-fitted to a cylindrical element 35 which is connected to asubstantially flat disk 30 by a plug clamp 34. This disk 30 constitutesthe base of the centrifugal fan 6 and is formed on its face or sideturned toward the oven door 17 with large radially extending vanes 8,and on its opposite face with small radial vanes 9. The outside edges ofthe vanes 8 are formed with a continuous ring 31 that has an innerperiphery axially received within a lip 33 on the hood walls 27. Anotherannular cylindrical flange 31 is provided spaced radially outwardly fromthe lip 33 to prevent the passage of air from outside of the rack intothe fan 6. In this manner the rims 31 and 32 flank the lip 33.

The oven is further provided with a conduit which passes through thechamber 4 and opens at one end to the ambient air in one position ofvalve 10' or to a source 10" of liquid nitrogen in another position ofthis valve, and at the other end into an opening formed in a mountingring 42 which is firmly mounted on the motor housing 40 and surroundsthe entire fan arrangement 8, 9, 11, and 12. The opening 51 in the rearwall 37 of the oven defines an annular space around the element 36.

In this manner, when the motor 2 turns, the vanes 11 draw fresh air inthrough the perforations 43 to cool this motor and its bearing 50, asshown by arrows 47. At the same time air from the tube 10 is deflectedoutwardly by the vanes 12 through the annular gap between the element 36and the element 42. The fan 6, which is rotationally coupled to the fan7 by the connector bolts 13, draws fresh air into the oven interiorthrough the gap 51 as shown by the arrows 44, and circulates gases inthe oven interior 54 by sucking them in axially (arrows 49) through therack 26, and expelling them radially as shown by arrows 48. The freshair between the vanes 12 and 9, which is fed in directly between thesevanes and pulled out in both axial directions, forms a very effectivegas barrier or gas lock against the passage of heat or contaminatedgases out of the oven interior and into the chamber 4. None of the airused to cool the motor 2, however, can enter the chamber 54 due to thearrangement of the conduit 10 and the relative fan capacities.

Simultaneously the vanes 8 circulate the gases in the oven to effect anexcellent distribution of heat during a self-cleaning, cooking orthawing operation.

Atop the oven is a horizontal conduit 5 which opens directly above thedoor 17 and serves as exhaust for the air displaced by the fan 7, whichair serves to form the gas barrier referred to above, and to cool themotor 2. A catalytic afterburner 15 is also mounted in the oven top walland has a outlet 16 fitted with metal plates pointed in the direction ofthe air stream of the exhaust conduit 5 so that the hot gases i.e. watervapor carbon dioxide etc. issuing therefrom are thoroughly diluted inthe air stream and rendered harmless. The current of gases issuing fromthe opening 59 of the conduit 5 are further upwardly deflected, as shownby arrow 60, by the air rising by convection in the gap 18 between thehot door plates 56 and 21.

The vanes 9 and 12 are so dimensioned relative to each other that theportion of the air sucked in through the tube 10 and into the oveninterior 54 is greater than that sucked in through this tube and thenceblown outwardly into the compartment 4. In the embodiment shown thevanes 9 have substantially the same total surface area as the vanes 12,but move at a greater angular speed due to their radial spacing from theaxis of rotation which is larger than that of the vanes 12. Thus, theair stream from the conduit 10 is split up, with the larger portiongoing into the muffle 54 due to the relative fan capacities which made apressure differential across the opening 5 1.

This apparatus is equally useful for the quick-freezing and storing ofcomestibles, since in this case the motor must also be thermallyprotected from the cold. With such an arrangement, liquid nitrogen fedinto the conduit 10 would be vented externally.

We claim:

1. An apparatus for thermally treating comestibles comprising:

means forming a generally closed chamber;

means for establishing a food-treatment temperature in said chamber; and

blower means having a drive motor outside said chamber and a rotorconnected to said motor and including centrifugal-fan means forcirculating gases in said chamber, for drawing air over said drivemotor, and for introducing gases into said chamber, said centrifugal-fanmeans including a pair of centrifugal fans, one of said fans beinginside said chamber and the other being outside said chamber, saidchamber having a wall formed with an opening, said rotor extendingthrough said opening, said fan in said chamber having a first faceturned toward said motor and bearing an array of radially extendingvanes and a second face turned away from said motor and bearing an arrayof radially extending vanes, said opening defining an annular gap aroundsaid rotor, said centrifugal-fan means further comprising meanscooperating with said vanes on said first face and forming a gas barrierat said gap for preventing issue of gases from said chamber through saidopening, the last-mentioned means including a conduit for feeding a gasto a location immediately adjacent said gap, whereby on rotation of saidfans said gas is drawn through said gap into said chamber by said arrayof vanes on said first face.

2. The apparatus defined in claim 1 wherein said fan outside saidchamber is formed with a first side turned toward said motor and bearingan array of radially extending vanes and a second side turned away fromsaid motor and bearing an array of radially extending vanes, whereby onrotation of said rotor said gas is drawn axially in two directions fromsaid location by said arrays of vanes on said first face and on saidsecond side to form said gas barrier.

3. The apparatus defined in claim 2 wherein said array on said firstface is of higher gas-displacing capacity than said array on said secondside to form a pressure differential across said opening constitutingsaid barrier.

4. The apparatus defined in claim 3, further comprising means forming acompartment adjacent said chamber and against said wall for forming anair-circulation path over said motor, said conduit passing through saidcompartment and having one end open to a supply of said gas and anotherend opening at said location.

5. The apparatus defined in claim 1, further comprising a pair ofmounting elements each connected rotationally to one of said arrays ofvanes and connecting means extending between said elements andconstituting the sole rotational coupling between said drive motor andsaid fan outside said chamber, said connecting means including aplurality of elongated connectors radially spaced from said axis andangularly spaced from one another, each connector having one end fixedin one of said elements and another end fixed in the other element.

6. The apparatus defined in claim 5 wherein said one of said elements isrotationally fixed on said array of vanes on said fan outside saidchamber turned toward said motor.

7. The apparatus defined in claim 5 wherein said connecting meansfurther includes a plurality of sleeves of insulating material eachsurrounding one of said connectors and having one end abutting one ofsaid elements and another end abutting the other of said elements. eachof said sleevooonheat-radiating vane.

8. The apparatus defined in claim 7 wherein each of said sleeves isformed with at least one heat-radiating vane.

9. An apparatus for the treatment of goods with a gas, comprising atreatment chamber having a wall provided with an opening, and a fanarrangement mounted in said opening, said fan arrangement including:

a first axial-intake radial-outflow blower in said chamber and rotatableto circulate a treating gas therewithin;

a second axial-intake radial-outflow blower rotatable about a commonaxis with said first blower and disposed axially rearwardly thereof withrespect to said chamber and having a smaller capacity than said firstblower for inducing a stream of treatment gas to flow into said chamber;

a third axial-intake radial-outflow blower rotatable coaxially with saidfirst and second blowers and disposed axially rearwardly of said secondblower for diverting a portion of said stream away from said chamber andcreating therefrom a cooling flow for restricting mixing of thetreatment gas with ambient air;

a fourth axial-intake radial-outflow blower rotatable coaxially withsaid first, second and third blowers and disposed axially rearwardly ofsaid third blower for generating a primary cooling flow of ambient air;and

an electric motor operatively connected to all of said blowers fordriving same and disposed in said primary flow. 10. The apparatusdefined in claim 9, further comprising duct means opening between saidsecond and third blowers for delivering said stream thereto.

11. The apparatus defined in claim 10, further comprising means forconnecting a source of freezing fluid to said duct means.

12. The apparatus defined in claim 10, wherein said duct means opensinto the atmosphere.

1. An apparatus for thermally treating comestibles comprising: means forming a generally closed chamber; means for establishing a food-treatment temperature in said chamber; and blower means having a drive motor outside said chamber and a rotor connected to said motor and including centrifugal-fan means for circulating gases in said chamber, for drawing air over said drive motor, and for introducing gases into said chamber, said centrifugal-fan means including a pair of centrifugal fans, one of said fans being inside said chamber and the other being outside said chamber, said chamber having a wall formed with an opening, said rotor extending through said opening, said fan in said chamber having a first face turned toward said motor and bearing an array of radially extending vanes and a second face turned away from said motor and bearing an array of radially extending vanes, said opening defining an annular gap around said rotor, said centrifugal-fan means further comprising means cooperating with said vanes on said first face and forming a gas barrier at said gap for preventing issue of gases from said chamber through said opening, the last-mentioned means including a conduit for feeding a gas to a location immediately adjacent said gap, whereby on rotation of said fans said gas is drawn through said gap into said chamber by said array of vanes on said first face.
 2. The apparatus defined in claim 1 wherein said fan outside said chamber is formed with a first side turned toward said motor and bearing an array of radially extending vanes and a second side turned away from said motor and bearing an array of radially extending vanes, whereby on rotation of said rotor said gas is drawn axially in two directions from said location by said arrays of vanes on said first face and on said second side to form said gas barrier.
 3. The apparatus defined in claim 2 wherein said array on said first face is of higher gas-displacing capacity than said array on said second side to form a pressure differential across said opening constituting said barrier.
 4. The apparatus defined in claim 3, further comprising means forming a compartment adjacent said chamber and against said wall for forming an air-circulation path over said motor, said conduit passing through said compartment and having one end open to a supply of said gas and another end opening at said location.
 5. The apparatus defined in claim 1, further comprising a pair of mounting elements each connected rotationally to one of said arrays of vanes and connecting means extending between said elements and constituting the sole rotational coupling between said drive motor and said fan outside said chamber, said connecting means including a plurality of elongated connectors radially spaced from said axis and angularly spaced from one another, each connector having one end fixed in one of said elements and another end fixed in the other element.
 6. The apparatus defined in claim 5 wherein said one of said elements is rotationally fixed on said array of vanes on said fan outside said chamber turned toward said motor.
 7. The apparatus defined in claim 5 wherein said connecting means further includes a plurality of sleeves of insulating material each surrounding one of said connectors and having one end abutting one of said elements and another end abutting the other of said elements.
 8. The apparatus defined in claim 7 wherein each of said sleeves is formed with at least oNe heat-radiating vane.
 9. An apparatus for the treatment of goods with a gas, comprising a treatment chamber having a wall provided with an opening, and a fan arrangement mounted in said opening, said fan arrangement including: a first axial-intake radial-outflow blower in said chamber and rotatable to circulate a treating gas therewithin; a second axial-intake radial-outflow blower rotatable about a common axis with said first blower and disposed axially rearwardly thereof with respect to said chamber and having a smaller capacity than said first blower for inducing a stream of treatment gas to flow into said chamber; a third axial-intake radial-outflow blower rotatable coaxially with said first and second blowers and disposed axially rearwardly of said second blower for diverting a portion of said stream away from said chamber and creating therefrom a cooling flow for restricting mixing of the treatment gas with ambient air; a fourth axial-intake radial-outflow blower rotatable coaxially with said first, second and third blowers and disposed axially rearwardly of said third blower for generating a primary cooling flow of ambient air; and an electric motor operatively connected to all of said blowers for driving same and disposed in said primary flow.
 10. The apparatus defined in claim 9, further comprising duct means opening between said second and third blowers for delivering said stream thereto.
 11. The apparatus defined in claim 10, further comprising means for connecting a source of freezing fluid to said duct means.
 12. The apparatus defined in claim 10, wherein said duct means opens into the atmosphere. 